1. Field of the Invention
The present invention relates to a passive optical network (PON) transmission system and a dynamic band assignment system to be employed in the same. More particularly, the invention relates to a dynamic band assignment system in the PON transmission system.
2. Description of the Related Art
Conventionally, a PON transmission system includes an optical network unit (ONU) processing portion for terminating on the side of a subscriber unit and an optical line terminal (OLT) processing portion terminating on the side of station equipment in an optical network.
As shown in FIG. 25, the ONU processing portion 6 is constructed with a buffer 61 for band restricted cell, a buffer 62 for non-band restricted cell, a grant identifying portion 63, a reception signal separating portion 64, a transmission signal multiplying portion 65, an idle cell generating portion 66 and a short cell generating portion 67.
The reception signal separating portion 64 receives a passive double star (PDS) down-link signal 101 and outputs a grant (transmission permission) signal 165. The grant identifying portion 63 receives the grant signal 165 and outputs a read signal 164 for band restricted cell upon identification of data grant and a short cell read out signal 170 upon identification of grant of short cell.
The buffer 61 for band restricted cell receives an input band restricted cell signal 161 as input to write the cell in a buffer (not shown), receives a read signal 164 for the band restricted cell as input to output an output band restricted cell signal 168 as read signal when the cell is present in the buffer and to output a read signal 163 for the remainder band restricted cell for enabling transmission of a buffer 62 for non-band restricted cell when the cell is not present in the buffer.
The buffer 62 for non-band restricted cell takes an input non-band restricted cell signal 162 as input to write the cell in the buffer (not shown), receives the read signal 163 as input to output an output non-band restricted cell signal 169 as read out signal when the cell is present in the buffer, and to output a read out signal 166 for the remainder non-band restricted cell when the cell is not present in the buffer.
The idles cell generating portion 66 takes the read signal 166 for the remainder non-band restricted cell to generate an idle cell for inserting in a remainder band to output an output idle cell signal 167. The short cell generating portion 67 takes the short cell read out signal 170 and a grant demand number signal 172 to generate a short cell at a read out timing of the short cell read out signal 170 to output an output short cell signal 171 to reset.
The transmission signal multiplexing portion 65 receives the output band restricted cell signal 168, the output non-band restricted cell signal 169, the idle cell signal 167 and an output short cell signal 171 and outputs a PDS up-link signal 102 by multiplexing the input signals.
As shown in FIG. 26, the OLT processing portion 7 is constructed with a reception signal processing portion 71, a short cell receiving portion 72, a grant generating portion 73 for the band restricted cell, a grant multiplexing portion 74, a transmission signal multiplexing portion 75 and a short cell grant generating portion 76.
The reception signal processing portion 71 receives a PDS up-link signal 103 and outputs an ONU identification number signal 173 and a short cell signal 171 per each cell. The short cell receiving portion 172 takes the ONU identification number signal 173 and the short cell signal 171 as inputs and outputs the grant demand number signal 172 by separating the grant demand number from the short cell.
The short grant generating portion 76 takes the short cell grant read out signal 176 as input and outputs the short cell grant signal 177. The grant generating portion 73 for band restricted cell takes the grant read out signal 174 for band restricted cell as input and outputs a grant signal 175 for band restriction cell.
The grant multiplexing portion 74 outputs the grant read out signal 174 for band restricted cell and the short cell grant read out signal 176, takes the grant signal 175 for band restricted cell and the short cell grant signal 177 as input to output the grant signal 178 as short cell grant. The transmission signal multiplexing portion 75 takes the grant signal 178 as input and outputs the PDS down-link signal 104.
In the conventional PON transmission system, when attempt is made to process a traffic required band restriction and a traffic unnecessary for band restriction in a single grant, high precision band assignment is necessary for the traffic which does not require band restriction equivalent to that for the traffic requiring the band restriction, and the process is complicate unless the band updating speed is adapted to a period of the traffic requiring band restriction.
On the other hand, in the conventional PON transmission system, when increasing and decreasing of the band updating speed by number of single grant irrespective of cell necessary for band restriction, UPC and shaper are required in ONU processing portion. Therefore, the conventional PON transmission system cannot assign the band at high speed.
Furthermore, in the conventional PON transmission system, a transmission method of the short cell or hand shake are not defined. Namely, no means for dynamically varying band between the ONU identification numbers is not defined.
Also, in the conventional PON transmission system, even if excessive packet cells are input in the ONU, irrespective whether the packet can be process or not in the OLT, the PDS has to acquire the band therefor.